I think you are correct that the brooch gifted by Miss Alice de Rotschild is one of the two pieces, but I am not certain it is the one at her throat. I suspect her gift is the one on her waist - and also worn in South Africa in 1901.

If the brooch from Lord and Lady Rotschild is included here, it must have been re-worked, as the diamond chains between the bow and the watch appears longer